Different subs will for sure produce a different sound.
Each size of sub (and, to a degree, each manufacturer) will have its own attributes.
For example, as a rule of thumb, the larger the cone the lower the sub will drop (lower notes).
So, certainly, your 12" will drop lower (and therefore produce deeper notes) than your 10"
The flip side is that the smaller cones (and again, this is rule of thumb) have a tighter control, hence will sound 'punchier'
What complicates issues slightly is levels of excursion (physical movement of the cone) - JL were always famous for a greater level of cone movement (forwards and backwards), which in turn allowed each woofer to produce a lower note than its chassis size would suggest, by physically moving more air than a comparable woofer of identical chassis size.
So, a JL 10" could, for example, drop as low as a Kenwood 12", but remain as punchy as a 10" simply by having a greater range of excursion.
Personally speaking, I've never dropped a 10" and 12" in the car at the same time.
I've run single tens in a sealed box, a ported box and even a bandpass box (that was shattering).
I've run two tens and two twelves, but my all time favourite set up was my dual voice coild single 10" JL sub, spanked by an Alpine V12 amp.
If your amp is 2 Ohm stable, hook them up and give them a whirl. You'll either like the two of them running together or not.
